The Open Cluster Chemical Abundances and Mapping Survey: VII. APOGEE DR17 [C/N]-Age Calibration

TL;DR

This paper establishes a new empirical [C/N]-age calibration for APOGEE DR17 giant stars, enabling chemical dating of field stars to study Galactic evolution, validated against asteroseismic ages.

Contribution

It provides the first robust [C/N]-age calibration for APOGEE DR17 giants, linking chemical abundances to stellar ages for Galactic archaeology.

Findings

Calibrated [C/N]-age relation valid for 8.6 to 9.8 log years.

Calibration consistent with Kepler asteroseismic ages.

Applicable mainly to metal-rich, disk giant stars.

Abstract

Large scale surveys open the possibility to investigate Galactic evolution both chemically and kinematically, however, reliable stellar ages remain a major challenge. Detailed chemical information provided by high-resolution spectroscopic surveys of the stars in clusters can be used as a means to calibrate recently developed chemical tools for age-dating field stars. Using data from the Open Cluster Abundances and Mapping (OCCAM) survey, based on the SDSS/APOGEE-2 survey, we derive a new empirical relationship between open cluster stellar ages and the carbon-to-nitrogen ([C/N]) abundance ratios for evolved stars, primarily those on the red giant branch. With this calibration, [C/N] can be used a chemical clock for evolved field stars to investigate the formation and evolution of different parts of our Galaxy. We explore how mixing effects at different stellar evolutionary phases, like the red clump, affect the derived calibration. We have established the [C/N]-age calibration for APOGEE DR17 giant star abundances to be $\log[Age({\rm yr})]_{\rm DR17} = 10.14 \, (\pm 0.08) + 2.23\,(\pm 0.19) \, {\rm [C/N]}$, usable for $8.62 \leq \log(Age[{\rm yr}]) \leq 9.82$, derived from a uniform sample of 49 clusters observed as part of APOGEE DR17 applicable primarily to metal-rich, thin and thick disk giant stars. This measured [C/N]-age APOGEE DR17 calibration is also shown to be consistent with astereoseismic ages derived from Kepler photometry.